These data, covering the full coastal area of Massachusetts, were created as part of the National Oceanic and Atmospheric Administration Office for Coastal Management's efforts to create an online mapping viewer depicting potential sea level rise (SLR) and its associated impacts on the nation's coastal areas.

The purpose of the Sea Level Rise and Coastal Flooding Impacts Viewer is to provide coastal managers and scientists with a preliminary look at sea level rise and coastal flooding impacts.

These polygon data depict the potential sea level rise inundation of coastal areas resulting from a projected 1 to 10 feet rise in sea level above current Mean Higher High Water (MHHW) conditions. Although the water surface mapped represents a particular increase in sea level in feet above MHHW, the actual cell values in NOAA's original raster data represent depth in meters.

The layer name for the SLR inundation data is NOAA_SLR_MA_POLY.

The process NOAA used to produce the SLR inundation data can be described as a modified "bathtub approach" that attempts to account for both local/regional tidal variability as well as hydrological connectivity. The process uses two source datasets to derive the final inundation rasters and polygons and accompanying low-lying polygons for each iteration of sea level rise: the Digital Elevation Model (DEM) of the area and a tidal surface model that represents spatial tidal variability. The tidal model is created using the NOAA National Geodetic Survey's VDATUM datum transformation software in conjunction with spatial interpolation/extrapolation methods and represents the MHHW tidal datum in orthometric values (North American Vertical Datum of 1988).

The model used to produce these data does not account for erosion, subsidence, or any future changes in an area's hydrodynamics. It is simply a method to derive data in order to visualize the potential scale, not exact location, of inundation from sea level rise.

See NOAA's detailed methodology for producing these data.

MassGIS downloaded all the data from https://coast.noaa.gov/slrdata/ and combined the separate inundation polygon feature classes into one feature class that contains no overlap. The processing included Dice (for faster drawing speed), Dissolve, Union, and field calculations. This combined layer was projected to the NAD 1983 Mass. State Plane Mainland Meters coordinate system.